1. Field of the Invention
This invention relates to a zoom lens system used for photo-taking in a 35 mm single lens reflex camera and having a shortest focal length of approximately 24 mm and a zoom ratio of 4:1.
2. Description of the Prior Art
In recent years, zoom lens systems used in single lens reflex cameras have become increasingly capable of wider angle and higher magnification photo-taking, and zoom lens systems having a shortest focal length of 28 mm to 35 mm and zoom ratios of 3:1 or 4:1 have been developed and sold commercially. Zoom lens systems of this type having a positive refractive power in the first lens unit (positive lens unit first type) are more effective in correcting aberrations. However, zoom lens systems of this type have the shortcoming that the shortest object distance cannot be made sufficiently short. In other words, if the conventional method in which focusing takes place by zooming out the first lens unit is employed, the illuminance at the shortest focal length drops markedly during focusing onto an object at a short distance. Consequently, where it is desired to obtain a sufficiently short object distance, the diameter of the first lens unit must be made quite large. In addition, in the telephoto side in which the relay magnification becomes large, since the variation in aberrations at the time of focusing onto an object at a short distance is large, the shortest object distance cannot be made sufficiently short.